In a multiple input multiple output (MIMO for short below) communications system, a multiplexing gain can be obtained by means of signal processing. The multiplexing gain is a capacity gain obtained when multi-stream signals are simultaneously transmitted in the MIMO communications system by using a same time-frequency resource. A value of the multiplexing gain is related to a channel rank. The multiplexing gain that can be obtained by means of signal processing increases with the rank. A channel rank is related to a signal propagation environment. If there are a wider variety of phenomena such as scattering and refraction in the propagation environment, a larger quantity of multipath components arrive at a receive end, and a channel rank corresponding to the multipath components is larger. However, when line of sight (LOS for short) propagation is performed between a base station and user equipment, that is, when there is a direct path between the base station and the user equipment, power of a signal from the direct path is far higher than power of a signal obtained from another path, and there is a relatively large correlation between subchannels. Therefore, a channel rank is relatively low, which is usually 1, that is, transmission of only one data stream signal is supported. As a result, a system throughput is limited.
In the prior art, a correlation between subchannels in a direct path scenario is reduced by increasing a transmission distance between two antennas at a transmit end, so that a base station and user equipment can perform multi-stream transmission with each other in the direct path scenario, to improve a system throughput. Specifically, as shown in FIG. 1, assuming that two antennas at a transmit end are t1 and t2, respectively, two antennas at a receive end are r1 and r2, respectively, a transmission distance D is a horizontal distance between the transmit end and the receive end, a distance between t1 and t2 is dt, and a distance between r1 and r2 is dr. In the prior art, D is increased to generate distance differences between t1 and r2 and between t2 and r2, so as to generate a phase difference between signals on the two paths. Therefore, r2 can distinguish between the signals on the two paths. According to this method, the receive end can distinguish between data streams on different paths, so that the transmit end and the receive end can perform multi-stream transmission in the direct path scenario.
However, in the prior art, when the transmit end and the receive end perform multi-stream transmission in the direct path scenario, locations of the transmit end and the receive end are constant. Consequently, the prior art cannot support multi-stream data transmission of a mobile user (a mobile receive end) performed in a direct path scenario, and has low applicability.